Ciprofloxacin: pH-dependent SERS signal and its detection in spiked river water using LoC-SERS

Monitoring the successful removal of antibiotics in waste and surface waters is of high interest to overcome the occurrence of antibacterial resistance in the ecosystem. Among the newly developed analytical methods, the lab-on-a-chip surface-enhanced Raman spectroscopic (LoC-SERS) technique has gained the interest of the scientific community in the last few years. Ciprofloxacin, a second-generation fluoroquinolone, is widely used and administered to patients in dosages up to 1000 mg. In addition, more than 50 % of the antibiotic is excreted in urine as the parental drug. Thus, ciprofloxacin in environmental samples may exceed the minimum inhibitory concentration (MIC) values. The present study aims to assess the potential of the LoC-SERS technique to detect the target analyte in spiked river water samples at MIC concentrations. As sample clean-up procedure, a simple filtration is proposed, while as SERS, active substrates silver nanoparticles prepared at room temperature are employed. Ciprofloxacin was successfully quantified in the 0.7-10 mu M concentration range with data that were measured on two different days. Furthermore, because of the low solubility of the antibiotic at the neutral pH range, insights into the effect of pH on the SERS signal of the target molecule are also presented.